Why might this cloth nappy have leaked?

[AngelDog]

DS had a big nappy leak last night and I can't work out why.

He is 21 m.o., a big child (2.5 stone - 99th centile and with chubby legs), a heavy wetter and sleeps on his stomach.

He was wearing a Little Lamb cotton nappy with 2 hemp boosters between the nappy and the wrap. The wrap was an XL Motherease Airflow.

The nappy and boosters have been washed often, and the nappy is the right size. They're all relatively new (about 4 months old).

He had a leak out of the top of the nappy at the side - above the leg.

None of the nappy was sticking out of the wrap and at least some of the nappy was dryish, so it wasn't volume of wee that was a problem.

Any ideas?

Can he get his hand in there and have a little rearrange? My ds is terrible for leaving his willy sticking up, and this results in massive leaks.The only way I managed to get round it is putting him in zip up fleece sleepsuits so there's no easy access for him

No, I don't think so - he was in a poppered vest (with vest extender), sleepsuit, a t-shirt on top and then a sleeping bag - all of which were soaking, of course.

It's possible I didn't check which way he was pointing though - that would make sense of where the leak was.